Many specialized terms and abbreviations are used in the communications arts. At least some of the following are referred to within the text that follows, such as in this background and/or the subsequent description sections. Thus, the following terms and abbreviations are herewith defined:
3GPP 3rd Generation Partnership Project
4-PAM 4-Pulse Amplitude Modulation
BPSK Binary Phase Shift Keying
cat E-DCH physical layer category (e.g., as specified in 3GPP 25.306)
E-DCH Enhanced Dedicated Channel
E-DPCCH Enhanced Dedicated Physical Control Channel
E-DPDCH Enhanced Dedicated Physical Data Channel
HSPA High-Speed Packet Access
IC Interference Cancellation
SF Spreading Factor
TF Transport Format
TTI Transmission Time Interval
WCDMA Wideband Code Division Multiple Access
Electronic communication forms the backbone of today's information-oriented society. Electronic communications are transmitted over wireless or wired channels using electromagnetic radiation, such as radio frequency (RF) transmissions, light waves, and so forth. Unfortunately, the availability and capacity of electronic communications are frequently limited by the interference and noise inherent in the communications channel between a transmitting device and a receiving device.
However, the utilization of a communications channel may be increased by adopting any of a number of different schemes. These schemes can enable more information to be communicated in a given spectrum allocation. Efficient utilization of spectrum can reduce the cost of communication services being provided, can enable richer communication services to be provided, or both. Such schemes can also strengthen or otherwise improve signal reception at a receiving device.
An example scheme entails interference cancellation (IC). For example, in future versions of mobile communication systems, IC may be used to achieve better performance in terms of peak data rates, system throughput, system capacity, and so forth. To cancel an interfering signal, the data bits (or at least modulation symbols) that it carries are first detected. The interfering signal is then regenerated at the receiver.
The detection may be performed before decoding (e.g., for pre-decoding IC) or after decoding (e.g., for post-decoding IC). The regeneration is performed to mimic how the transmitted bits arrive at the receiver. This regeneration typically involves going through the operations performed at the transmitter (e.g., reproducing what the transmitter did to the data bits) and channel filtering (e.g., reproducing what the channel has done to the data bits).
Pre-decoding IC therefore entails cancelling an interfering signal before decoding. In this case, the transmitted bits carried in the interfering signal are detected after demodulation, but before decoding. Pre-decoding IC is attractive due to its low latency, which pre-decoding IC offers because there is no need to wait for the receipt of a complete codeword. This low latency advantage is especially pronounced for the case of, for example, a 10 millisecond (ms) Transmission Time Interval (TTI). Typically, for pre-decoding IC the desired latency is on the order of a few slots.
With pre-decoding IC, the interferer is not decoded before the cancellation is performed. Some knowledge of the interferer, however, helps to better detect the interfering signal. For example, if the receiver knows the modulation format used by the transmitter, the transmitted bits may be better detected. Further, a modulated symbol is spread by a channelization (or spreading) code according to a spreading factor (SF). Thus, the receiver uses the SF and the channelization code at the transmitter to recover a modulated symbol.
Herein, the term “transport format” (TF) refers to a combination of the modulation, the SF, and the number of channelization codes that are used by the transmitter. A relevant issue therefore relates to how the TF can be obtained to facilitate the detection of the transmitted bits of an interfering signal.
According to the Enhanced Dedicated Channel (E-DCH) provision of 3GPP release 6, the TF information is carried in a control channel named the Enhanced Dedicated Physical Control Channel (E-DPCCH). Unfortunately, for 10 ms TTI (i.e. 15 WCDMA slots), an E-DPCCH message is also spread over 10 ms. Consequently, the E-DPCCH can only be received very reliably after 10 ms. This means that within the desired latency of pre-decoding IC (e.g., usually within a few or several slots), the TF cannot be detected reliably through the reception of E-DPCCH.
Early E-DPCCH detection is possible provided that E-DPCCH is temporarily boosted in power. However, the E-DPCCH boosting feature is not available for 10 ms TTI. Early E-DPCCH detection is also possible if the E-DPCCH power is steadily increased, but this causes additional interference in the system.
Thus, the current state of the art fails to offer an effective or prudent approach to acquiring the TF in an acceptable timeframe. Consequently, there is a need to address these deficiencies so as to enable pre-decoding IC. Such deficiencies and other needs are addressed by one or more of the various embodiments of the present invention.